This invention relates to an image recording apparatus utilizing an electrophotographic system such as a laser beam printer.
Conventionally, there is known an image recording device utilizing an electrophotographic system in which a surface of a photoconductive drum is exposed to light to form a latent image on the drum surface. Toner then applied to the latent image to develop the image, and the developed image is transferred onto a recording sheet and is fixed by a fixing unit. Such an image recording device is chiefly employed in copying machines. In recent years, however, the image recording device has been utilized in printers and the like for printing the output from a computer, one of which is a laser beam printer.
The laser beam printer comprises, as one example is illustrated in FIG. 1, a photoconductive drum 1. Arranged about the photoconductive drum 1 in due order in rotational direction thereof are a charging station A, an exposure station B, a developing station C, a transferring station D, a toner-cleaning station E, and a discharge station F.
The arrangement is such that at the exposure station B, the laser beam scans the surface of the drum 1 which has been uniformly charged at the charging station A, to thereby form a latent image on the charged drum surface. Toner is then applied at the developing station C to the latent image to develop the same. Subsequently, the developed toner image is transferred at the transferring station D onto the recording sheet P which travels at a velocity identical with the circumference speed of the photoconductive drum 1.
The recording sheet P, carrying the toner image transferred thereon at the transfer station D, is guided and/or conveyed by guide rollers to a fixing station G. The recording sheet P is heated or pressed at the fixing station G for the toner image to be fixed on the surface of the recording sheet P.
When the recording sheet is arranged so that it is ejected with its image-carrying side up (with the printed side up) as shown in FIG. 1 (so-called "faceup ejecting"), the recording sheet is readily guided by holding the underside (i.e. undersurface) thereof without the toner image as far as the conveyance direction is concerned.
However, printers are normally used to print out the sheets continuously and if the sheets are ejected with the image-carrying surfaces up, they will be stacked in inverted order of pages. As a result, it has been desired for the laser beam printers to be able to exhaust the sheets with their image-carrying surfaces down (so-called "facedown ejecting") so that the sheets are stacked in the order of pages.
The functional stations (including the charging, exposure, developing, transferring, toner-cleaning and discharge stations, A, B, C, D, E and F), respectively with respect the photoconductive drum are disposed in such a manner as to arrange the transfer unit above the photoconductive drum. The recording sheet with the printed side down can thus be exhausted in facedown condition.
With this arrangement, however, the toner image is transferred to the undersurface of the recording sheet and accordingly the undersurface of the recording sheet cannot be used to hold it for feeding from the transfer station to the fixing station. The problem is that the recording sheet cannot be guided to the fixing unit properly.
What has heretofore been proposed to meet the foregoing requirement is that the recording sheet is turned upside down before being exhausted by guiding the recording sheet along a sheet exhaust path inversely extending from the fixing station inside the printer up to the same side as the sheet introduction side.
However, with the aforementioned arrangement, the recording sheet feed path inside the printer becomes long and complicated, which causes jamming and so on, and further, the printer tends to be large-sized.